According to their NMO-IgG serostatus, we classified definite and high risk NMO patients into three different groups (Table 2): 1) seronegative patients (n = 10); 2) patients with Abs against M-23 AQP4 but not against full length AQP4 (n = 15); and 3) patients with Abs against both AQP4 isoforms (n = 31). The gene discussed is AQP4; the disease is neuromyelitis optica.